Modern wireless telecommunication devices sometimes require the simultaneous transmission of signals corresponding to different wireless communication standards. Those wireless communications standards require the transmission of signals with a constant or non-constant envelope depending on the modulation type used for the standard. As a consequence, the signals according to different communication standards often require separate transmission paths to satisfy either high efficiency at saturated output power for signals with constant envelope or high linearity for signals with non-constant envelope.
For example, signals with constant envelope may comprise data content according to the GSM850/900 or the DCS1800/PCS1900 communication standard. Modulation types resulting in signals with a non-constant envelope are used by the communication standards according to the WCDMA LB, WCDMA MB or WCDMA HB standard. GSM950/900 is an abbreviation for the “General System for Mobil Communication”, while the numbers refer to the center frequency in MHz of the used channel. PCS1900 is the “Personal Communication Service” at a frequency of 1900 MHz used in North America. The Digital Cellular System (DCS) is based on the PCS standard and used outside North America. The communication standards GSM/EDGE, PCS and DCS are part of the second or 2.5 generation of cellular communication networks, also called 2G and 2.5G, respectively. WCDMA stands for “Wideband Code Division Multiple Access” and is a type of the third generation of cellular communication networks and standards (3G).
Due to external, often unknown parameters, for example the distance between a base station and a mobile station, the power amplifiers of the transmitter paths have to deliver a wide range of different output powers. The different communication standards themselves specify different maximum output powers which the power amplifiers in the transmitter paths have to deliver. Further, there is a trade-off between efficiency in high-power applications and linearity of the used amplifiers. Normally, a higher linearity of the amplifier will result in a lower maximum output power and vice versa. Furthermore, the linearity at low output power may differ from the linearity at high output power. Therefore, wireless transmitter architecture often includes a plurality of different power amplifiers in different transmitter paths for each of the above-mentioned standards. Despite the excessive size and costs of such arrangements, talk and battery time is also of some importance.
As a result, there is a desire to further improve already existing arrangements to reduce size and costs.